2021 Volume 64 Issue 4 Pages 223-233
High thrust propulsion systems that can be used in small spacecraft are urgently needed to expand the use of small spacecraft. This study proposes a hybrid thruster for small spacecraft using wire-shaped magnesium as a fuel and water as an oxidizer. “Hybrid thruster” means that the in-space propulsion system generates thrust using a chemical reaction between a solid fuel and a vapor oxidizer, such as those utilized for hybrid rockets. Both magnesium and water are very safe, highly available, and very storable. To assess the feasibility of a hybrid thruster, we carried out experiments utilizing magnesium-wire combustion in water vapor at a pressure lower than the atmosphere, and estimated the input power for ignition, ignitability, and the average magnesium mass consumption rate. Then, propulsion performances were calculated using the experimental results, which show there is an input power of 2–3 W, with higher ignitability and a lower average mass consumption rate for thinner magnesium wires. The calculated specific impulse achieved its maximum at 323 s, with a mass mixture ratio of 1.25. At that mass mixture ratio, the calculated thrust using magnesium wires having diameters of 0.5 mm and 0.8 mm was 49.8 mN and 68.5 mN, respectively. Additionally, the applicability of the hybrid thruster was shown through a case study considering an existing deep-space misson.